Re: Testing Knock Sensors

[Paul Nicholson <paul@eisusa.com>]

A knock sensor is piezo-electric. It is non-conductive material and when it is excited, it generates a voltage. These materials are used for igniters on gas grills and lighters by employing a spring and hammer mechanism to whack it good and make an electrical spark.

You won't  be able to detect anything with a resistance meter. A good sensor should read open. Like the man said, stick it on a scope. In lieu of a scope, you may be able to detect an AC signal with a volt meter if you hook up to the sensor and excite it with a vibrating source, like a Dremel marking tool, however be warned that the signal level from these transducers is fairly low.

The possibility exists that the sensitive element has experienced a failure that causes it to generate less that the required signal, a partial crack for instance, and just because you see a signal, it still could be defective.

Paul

At 21:42 -0500 12/2/99, ozitzmann@atmi.com wrote:
>Thank you for your input.  Not to be too technical, but there are two types of
>knock sensor faults - 2143 (excessive knock) and 2144 (open or short circuit).
>I have 2144.  When testing the three wires from the sensor, I get an open
>circuit between all three, as well as between each and ground (no measurable
>resistance value).  Is that normal?  I will check the torque this weekend, but I
>assume 2144 would not be the fault if it was incorrectly torqued?!?!
>
>oz
>
>'90 200 Avant